1. Field of the Invention
The invention relates to an IGZO-based oxide material and a method of producing an IGZO-based oxide material.
2. Description of the Related Art
In recent years, amorphous In—Ga—Zn—O-based homologous oxide materials (hereinafter, referred to as “IGZO-based oxide materials” or simply as “IGZO” sometimes), represented by a composition formula In2-xGaxO3(ZnO)m (0<x<2 and m is a natural number) in a crystalline state thereof, have been attracting attention.
Hosono et al. from Tokyo Institute of Technology reports that the amorphous IGZO-based oxide materials exhibit a value of electrical resistivity similar to that of a semiconductor and can be formed into a film at room temperature, and that these materials can achieve a mobility that is equal to or higher than that of amorphous silicon (Hosono et al., Non-patent Document 1, Nature, 432 (2004) pp. 488-492).
In particular, amorphous IGZO-based oxide materials represented by the above composition formula in which m=1 are highly promising material systems because of their great amount of ratio of overlapping of electron orbits between In—In which is considered to contribute to the conduction of electrons.
Research and development on the amorphous IGZO-based oxide materials are being intensely conducted with respect to the use of these materials as, for example, an effective material for an active layer of a thin film transistor (hereinafter, referred to as “TFT” sometimes).
On the other hand, IGZO-based oxide materials having a crystalline structure are described, for example, in the following literatures.
Non-patent Document 2 (Journal of the American Ceramic Society, 82 (1999) pp. 2705-2710) describes a method of producing a crystalline IGZO-based oxide material in which m=1, in which a mixture of raw materials including In, Ga and Zn is annealed at 1350° C. or higher, and then rapidly cooled down from this extremely high annealing temperature. The document also discloses that the solid solution range of Ga (range of x) is from 0.66 to 1.06.
Further, Japanese Patent No. 3947575 discloses a process of subjecting a crystalline IGZO-based oxide material in which m=1, which is obtained by annealing at certain conditions, to a reduction heat treatment at a certain temperature in a hydrogen or argon atmosphere.
In this regard, in many of electron-conductive oxide materials properties including IGZO, properties that are unique to these materials are significantly affected by the value of an amount of oxygen vacancy δ. When the value of δ is great, a large number of carriers (electrons) are generated and a “degenerate semiconductor”, having a Fermi level within the conductive band, is formed. In other words, the oxide material in this state is a conductor that exhibits metallic conductivity. On the other hand, when the value of δ is small, generation of carriers can be suppressed and the oxide material can exist as a semiconductor. The above fact indicates that the nature of an oxide material may greatly vary from a conductor to a semiconductor, depending on the value of oxide deficit amount δ.